Sprinkler heads are installed in the ceiling surface or wall surface in a building and have at one end thereof a nozzle that can be connected to piping leading to a water supply source, and a heat sensitive operating portion is provided at the other end. At normal times, the heat sensitive operating portion supports a valve that closes the nozzle.
Examples of the above-described sprinkler heads include concealed type sprinkler heads that are flush-mounted in the ceiling surface or wall surface and covered with a cover plate.
Concealed-type sprinkler heads are used as aesthetically excellent sprinkler heads and include that described in Patent Literature 1. In the concealed type sprinkler head of Patent Literature 1, a cylindrical member is provided outside a so-called frame-yoke-type sprinkler head in which a horseshoe-shaped frame extends from the end of a nozzle and a deflector is installed on the extension of the nozzle, and an engaging portion to be engaged with a cover plate is provided in the lower part of the cylindrical member.
The sprinkler head shown in FIG. 6 has the same structure as the concealed type sprinkler head of Patent Literature 1. A cylindrical member A is provided outside a frame-yoke-type sprinkler head SH (hereinafter referred to as “sprinkler head SH”). A cylindrical retainer B to which a cover plate P is bonded with a low melting alloy is connected to the lower part of the cylindrical member A.
As the structure of the connection between the cylindrical member A and the retainer B, a spiral groove A1 formed in the lower part of the cylindrical member A and a protrusion B1 formed on the outer peripheral surface of the retainer B are configured to be engaged with each other.
As shown in FIG. 6, the sprinkler head SH, the cylindrical member A, and the retainer B are disposed in the ceiling. Only the cover plate P is disposed close to the ceiling surface. The cover plate P is connected to the retainer B with a low melting alloy and therefore drops due to the heat at the time of a fire. By the drop of the cover plate P, the sprinkler head SH is exposed.
Following the exposure of the sprinkler head SH, a heat sensitive portion G of the sprinkler head SH operates and breaks, and opens the valve inside the sprinkler head SH, and thereby water is sprinkled from the sprinkler head SH and extinguishes the fire.    Patent Literature 1: U.S. Pat. No. 4,014,388 specification